It is known that bubbles form in divers using currently-accepted diving schedules and that undesirable hematological sequelae result from these non-symptomatic bubbles. This indicates a need for more precise definition of critical conditions in vivo required for phase separation so that decompression procedures can avoid bubbles rather than waiting until bends are evident. These conditions can best be determined in fish due to their unique physiology--freedom from the thermal problems found in air breathers, suitability for being subjected to changes in hydrostatic and gas pressures independently, and ability to voluntarily shorten their blood clotting time during stress. The interrelationships of bubble formation and hematological sequelae will then be investigated through combined experiments monitoring bubble and clot formation in the same fish to identify hematological changes which can be used as sensitive indicators of decompression stress from precisely defined supersaturations.